In internal combustion engines, in particular in piston engines, mechanical driving power is generated by burning a fuel. In so doing, a majority of the chemical energy contained in the fuel is released as heat, which frequently remains unused. Frequently, even a portion of the usable driving power must be used for cooling the internal combustion engine and its units. With a waste heat utilization device, the waste heat occurring in an internal combustion engine can be used, for example, in order to provide further driving power or electrical energy. Hereby, the overall energy efficiency of the internal combustion engine can be improved.
Such waste heat utilization devices are known for example from EP 2 573 335 A2 and from DD 136 280.
Waste heat utilization devices can be configured as a circuit process in the form of a so-called Carnot process. The so-called Clausius-Rankine process is a special Carnot process. In such a Clausius-Rankine process, a working medium circulates in a waste heat utilization circuit. In the waste heat utilization circuit there is situated an evaporator for evaporating the working medium, which extracts heat for this from the internal combustion engine. Downstream of the evaporator there is situated in the waste heat utilization circuit an expansion machine for the relieving of the working medium to a low pressure. Downstream of the expansion machine there is situated in the waste heat utilization circuit a condenser for the liquefying of the working medium. Downstream of the condenser, a compression machine is to be found in the waste heat utilization circuit for compressing the working medium to a high pressure. From the compression machine, the working medium arrives at the evaporator again. In relieving the pressure of the working medium in the expansion machine, thermal energy is converted into mechanical driving energy, which can be used directly as mechanical driving power, or can be converted into electrical energy by means of a generator. The heat for the evaporating of the working medium can be extracted for example from the waste gas of the internal combustion engine. A pump arranged downstream of the condenser in the waste heat utilization circuit serves for the conveying of the working medium.
It proves to be disadvantageous in such a conventional waste heat utilization circuit that undesired cavitation effects can be brought about through the working medium in the pump. These can lead to a damage to the components of the pump which are mechanically in contact with the working medium. In extreme cases, this can even result in a destruction of the pump.
It is therefore an object of the present invention to create a device for use in a waste heat utilization circuit, which counteracts the formation of undesired cavitation effects in the pump which is driving the working medium.
This problem is solved by the subject of the independent claim(s). Preferred embodiments are the subject of the dependent claims.